1. Field of the Invention
The disclosure is generally related to electric drivetrains, and particularly to electric drivetrains comprising an alternating current (AC) electric motor powered by a direct current (DC) power source via one or more inverters.
2. Description of the Related Art
In contrast to an internal combustion engine, an electric motor can operate over a very wide range of rotational speeds. Thus, a multiple-speed transmission is not required in a vehicle propelled by an electric motor (e.g., electric vehicle or hybrid vehicle), as is the case for an internal combustion engine in order to convert the relatively narrow speed range of an internal combustion engine to a wider range of vehicle speeds. Consequently, electrically propelled vehicles may employ simple transmissions, for example, single-speed transmissions.
A simple transmission has several benefits, including reduced number of parts, reliability and low cost. However, simple transmissions may be subject to “backlash” where the mating teeth of two gears (e.g., a driving gear and a driven gear) are not in contact when the driving gear begins to move. When such a backlash condition occurs, the driving gear accelerates quickly before its teeth are in contact with the teeth of the driven gear. The result may produce a significant impact between the teeth of the gears, creating excess forces and consequently wear on the teeth of the gear. The impact may also introduce a significant torsional oscillation into the vehicle's drivetrain, particularly around the torsional resonant frequency of the drivetrain. The oscillation in turn may lead to customer dissatisfaction with the drivability of the vehicle.
Some electric vehicles employ vibration compensators to overcome the torsional vibration caused by gear backlash and chassis dynamic. Such vibration compensators typically employ a band pass filter operating on a speed signal and centered on the natural resonance frequency of the drive or power train. The output of the filter is proportional to the degree of vibration, and is subtracted from the requested torque command to compensate for the vibration.
Such vibration compensators are inadequate in a number of different circumstances, for example, where available power or ability to produce additional torque are limited. A system that can provide vibration compensation over a wider range of conditions may advantageously increase reliability and/or improve customer satisfaction.